In general, in a transmission device for a motor vehicle engine or the like, in which mechanical power is transmitted by a medium such as a chain, belt or the like, a movable or fixed guide is attached to a body frame, such as an engine block wall, by a mounting bolt, a pin or the like. The chain, belt, or other power transmission medium, travels in sliding contact with the guide.
In the case of a movable guide, which may be in the form of a tension lever or the like, the guide provides the power transmission medium with appropriate tension to prevent transmission failure resulting from excessive stretching, or excessive loosening, of the power transmission medium. A fixed guide, such as a guide rail or the like, limits the power transmission medium to a predetermined traveling path to prevent vibration noise, side vibration, and disengagement.
FIG. 13 illustrates an example of a conventional synthetic resin guide 100 for a tensioner lever. The guide 100 comprises a slide rail 101, which is in sliding contact with a traveling chain C, and a rail-supporting member 102 provided on the back side of the slide rail 101. The rail supporting member 102 includes a boss 102a having a mounting hole 103 for pivoting attachment to an engine block wall. The rail supporting member also includes a tensioner abutting portion 102b, which cooperates with a tensioner (not shown) for providing appropriate tension to prevent transmission failure resulting from excessive stretching, or excessive loosening, of the chain. The synthetic resin guide 100 includes a plurality of thick reinforcing ribs 102c, each formed at suitable intervals along the rail supporting member 102, to enhance the mechanical properties and toughness of the guide 100.
The conventional synthetic resin guide 100 has several problems preventing it from exhibiting good mechanical properties and toughness. When the guide is injection-molded from an injection gate provided on one end portion of the guide, the reinforcing ribs 102c extend substantially perpendicular to the direction of injection of the synthetic resin P. As a result of the orientation of the reinforcing ribs, the flow of the injected synthetic resin P, which, as shown in FIG. 14, comprises a skin layer-forming resin P1 and a core layer-forming resin P2, exhibits a stagnant fluid state within and around the interior of the reinforcing ribs 102c. The residence, eddy flow, and turbulent flow of the resin P prevent the resin from achieving a strain-free molecular orientation in the interior of the reinforcing ribs 102c. Consequently, the peripheral portions of the ribs are solidified in an strained state. The orientation strain not only causes cracks due to loading during power transmission, but also causes thermal shrinkage resulting from a non-crystalline region in the synthetic resin P. Accordingly, strains such as warpage, torsion and the like occur in a high temperature environment such as in an automobile engine, and the guiding function is not entirely satisfactory.
Referring to FIGS. 15 and 16, when a synthetic resin P, composed of a glass fiber reinforced resin (consisting of a skin layer forming resin P1 and a core layer forming resin P2) is used, ideal mechanical properties and toughness are exhibited when the reinforcing glass fibers F contained in the core layer forming resin are oriented in a direction substantially parallel to the slide rail 101. However, as described above, since the reinforcing rib portions 102c extend substantially perpendicular to the direction of injection of the synthetic resin P, the resin is in a stagnant fluid state in the interiors of the respective reinforcing ribs 102c, and in the peripheral portions thereof. Residence, eddy flow, turbulent flow and the like are generated in the fluid resin, and, as a result, as shown in FIG. 16, the orientation of the glass fibers is disturbed. Thus, in spite of the mixing of glass fibers F in the synthetic resin P to increase the strength of the guide, ideal strength cannot be achieved.
Furthermore, since the reinforcing rib portions 102c impair the flow of the glass fiber-reinforced synthetic resin P, moldability during injection molding is unsatisfactory. Thus, glass fibers F cannot be dispersed in such a way that they are oriented in a specified direction, and cannot be mixed uniformly in the resin. To solve this problem, changing the injection conditions has been tried. However, a higher injection pressure and a longer injection time are required, thereby increasing the cost of injection molding.
Accordingly, objects of the invention are to solve the above-mentioned problems encountered in the prior art, and to provide a synthetic resin guide for a transmission device including reinforcing portions, which exhibits greater strength and toughness, and in which strains such as warpage, torsion and the like in a high temperature environment are significantly reduced.
The synthetic resin guide in accordance with the invention comprises an elongated rail for longitudinal sliding engagement with a power transmission medium, and a rail supporting member molded as a unit with the rail. The supporting member comprises a plurality of reinforcing ribs which support the rail. These ribs are distributed along the length of the transmission device from a location adjacent one end of the rail to a location adjacent the opposite end of the rail. The guide is formed by injection molding, and, in order to achieve the above-mentioned objects, the reinforcing ribs extend in directions such that the flow of synthetic resin during injection molding substantially follows the longitudinal directions of the reinforcing ribs. Preferably, the synthetic resin is a glass fiber reinforced resin. The synthetic resin guide in accordance with the invention, may be either a fixed guide or a movable guide.
In order for the reinforcing ribs to extend in a direction following the flow of resin during injection molding, any arrangement such as an S-shaped arrangement, a curved arrangement, a truss-shaped arrangement, a vein-shaped arrangement, a honeycomb-shaped arrangement, or the like, may be used.
The injection molding process used to produce the synthetic resin guide according to the invention can be an injection molding process in which resin processing is integrally carried out from one end portion in a longitudinal direction of the guide toward the other end portion. For example, any process such as a typical injection molding process using a single synthetic resin, a two-color injection molding process using two kinds of synthetic resins, a sandwich injection molding process in which a core layer resin is injected inside a skin layer, or the like, may be used.
According to the invention the reinforcing rib portions which supports the slide rail extend in directions following the flow of synthetic resin during injection molding of the guide. Thus the reinforcing rib portions behave as auxiliary flow paths, which lead the synthetic resin injected during the injection molding of the guide from one end portion in a longitudinal direction of the guide toward the other end portion, so that injected synthetic resin flows throughout the guide without significant flow resistance, so that the injected synthetic resin flows smoothly to the end of the synthetic resin guide.
Since the synthetic resin is fully molecularly-oriented when solidified, the crystal region of the synthetic resin is increased and thermal shrinkage of the guide is reduced. Furthermore, the pressure required for injection molding of the guide can be reduced to a lower level than in the conventional case, and the injection time can also be reduced.